Any existing electronic component is characterized by electric power absorption—in general, proportional to the product of a current crossing it and a voltage that develops across its terminals—during an operation thereof. A portion of such absorbed electric power is lost as heat according to the principles of thermodynamics. In particular, heat is generated in “active” regions of the electronic component, i.e., where the flow of electric current occurs (for example, considering a MOSFET transistor, in a region below a control terminal and in regions forming the conduction terminals thereof). The heat generation concentrated in active regions causes a temperature rise of the electronic component. The temperature of the active regions of the electronic component, better known as junction temperature, is a parameter that strongly affects the operation of the electronic component. In particular, a threshold voltage of the electronic component, according to which the intensity of the current thereof is controlled, is inversely proportional to the junction temperature; consequently, for the same applied control voltage, the electronic component draws an electric current flow that increases with the rising of the temperature. It is also known that, with the rising of the junction temperature, there also occurs an increase in the electric resistivity of the electronic component. Consequently, the electronic component dissipates, due to the Joule effect, an increasing electric power between its terminals, and this leads to an ever rising junction temperature; in other words, it is established a positive feedback that may cause damage or even destruction of the electronic component due to a too high junction temperature. In addition, with the increasing of the junction temperature of the electronic component there is a reduction of the reliability thereof (i.e., the probability of occurrence of a structural damage during operation increases) and in general of its useful life (i.e., the time during which the electronic component works properly).
The ongoing miniaturization process of the electronic components (basically a reduction in the size of the electronic component, in particular of the active regions), makes it very important to limit the rise in the junction temperature within an acceptable range. Indeed, for the same absorbed electric power, the smaller the size of the active area of the electronic component the greater and the more rapid the rise in the junction temperature thereof (since the consumption of electric power is concentrated in a smaller volume). This is particularly important in electronic components belonging to the field of the “power electronics”, i.e., electronic components designed to operate at high voltages and currents with respect to standard electronic components (for example, with operating voltages of the order of hundreds of Volts and/or with operating currents of the order of tens of Amperes), which are used in circuits of apparatuses belonging to various fields of application, for example, from personal computers to electro-mechanical equipments (computers power supply circuits, electric motor actuators, inverters for photovoltaic panels, etc.).
Heatsinks are known and widely used to limit the rise of the junction temperature in electronic components. A heatsink is an element consisting of one or more elements of thermally conductive material (e.g., aluminum Al), which is fixed (typically by gluing and/or double-sided adhesive material tapes) to a package of the electronic component. The package comprises a substantially insulating body (usually made of plastic or ceramic) and contact pins (for connecting the electronic component to tracks of an external circuit), and it is intended to embed and protect a chip of semiconductor material in which the electronic component is integrated.
Alternatively, the insulating body of the package may also comprise an opening—typically formed in an upper free surface of the insulating body opposite a mounting surface towards which the pins are orientated—to expose a dissipation plate (also made of thermally conductive material). The dissipation plate is connected to the chip for improving the heat exchange with the external environment. The heatsink may be attached directly to the dissipation plate by means of double sided adhesive tapes or glues with high thermal conductivity coefficient, which conform the contact surface, thus facilitating heat exchange between the plate and the heatsink (thanks to the greater thermal conductivity of the materials constituting the dissipation plate and the heatsink contacting each other with respect to the plastic ones constituting the insulating body).
In more detail, the heatsink facilitates the transfer of heat by conduction (thanks to its good thermal conductivity) from the chip to itself. In addition, the heatsink is usually formed with a structure designed to facilitate a transfer of heat by convection (for example, with a plurality of fins extending from a base through which the heatsink is fixed to the insulating body or to the dissipation plate) to the environment outside the package (i.e., transferring heat to the medium that surrounds the package, for example, air). In this way, suitably sized heatsinks allow for keeping the junction temperature below a safety temperature.
However, heatsinks suffer from a major disadvantage, particularly when applied to small packages (e.g., for embedding miniaturized electronic components). Indeed, the heatsinks tend to be mechanically unstable, once fixed to the package. This is due to the fact that by reducing the size of the packages, an available mounting surface is proportionally reduced. This reduced mounting surface may be insufficient to ensure good mechanical stability of the heatsink on the package; therefore, the heatsink might separate from the package as a result of mechanical stresses to which it may be subject. In addition, the weight of the heatsink and the mechanical stresses might cause a deterioration, or even a rupture, of contacts formed between one or more pins of the package and the corresponding conductive tracks of the board to which they are attached, up to causing their detachment and the malfunction of a circuit in which the electronic component is used.